appendix A • EC-2 96kHz A/D/D/A upgrade
EC-2 Manual A-11
Using the HD24/EC-2 withcomputer workstations anddigital mixers
Because the EC-2 upgrade provides 24 high quality
inputs and outputs, it can be used as an external
converter to extend the number of analog inputs
and outputs of any computer workstations and
digital mixers that feature an ADAT Optical
interface. When using it as an A/D converter, press
the ALL INPUT button with INPUT SELECT set to
ANALOG; when using it as a D/A converter, set
INPUT SELECT to DIGITAL.
Remember that for an input or output to be active,
the current Song must be initialized for the
proper number of tracks, even if you’re not
recording or playing back the HD24 itself.
For more information see pages 39-40 in chapter 3 of
the HD24 manual, Basic Recording and Playback.

High sample rate operation

If you want to use the HD24/EC-2 with a
workstation or digital mixer at the 88.2/96kHz
sampling rates, the question to ask the
manufacturer of the other unit is: “does this
support the ‘sample-split’ implementation for
96kHz audio transmission, with 4 channels of
96K/24-bit audio per ADAT Optical cable ?” The
details of this format are outlined by the Alesis
Optical Interface Specification Addendum,
February 2001. If it doesn’t, instead of treating each
lightpipe as a high-speed 4-channel interface, the
workstation will use it as the traditional standard-
speed ADAT Optical 8-channel interface. If that’s
the case, you’ll get apparently “duplicate” signals
on the device receiving signal from the HD24 in 96
kHz mode: Track 1 will appear on channels 1 and 2
of the digital mixer or workstation, etc.
In some cases, you need to manually set the other
device to send and receive a 96k signal on the
ADAT lightpipe. In other cases, you may need to
upgrade the software or hardware of the unit so it
can interface digitally. Contact the manufacturer of
the workstation or mixer for more information.

Latency

Every digital conversion requires a certain amount
of time, although the time delay involved is usually
less than the time it takes sound to travel one foot
through the air. However, if you have a digital
workstation that allows compensation for input and
output delays, see the Specifications section on page
13 of this manual for latency figures. In most cases,
this is only critical when you’re using different
interfaces simultaneously (for example, the analog
inputs of a computer interface plus its ADAT
Optical inputs receiving the output of the HD24). In
extremely critical applications, you should test
latency matching by using a 20kHz burst tone sent
to all inputs simultaneously, viewing the start point
of the waveform bursts on the screen of a digital
audio workstation, then adjusting the start times of
all tracks to compensate.